Phase detectors are typically used to detect phase of an input signal having a positive voltage phase and a negative voltage phase. While phase detectors are found in a myriad of electronic applications, one typical application of phase detector is found in shunt regulator rectifier. A schematic diagram illustrating a conventional shunt regulator rectifier 100 configured to convert a 3-phase AC input into a DC output is shown in FIG. 1. As shown, a first rectification unit 110, 112, 114 and a second rectification unit are connected to each of the phase R, Y, B of the AC input. The first rectification unit has a FET or a diode configured to rectify positive cycle of the AC input. The second rectification unit has a MOSFET 120, 122, 124 configured to rectify negative cycle of the AC input and to shunt the AC input in case output voltage of the shunt regulator rectifier exceeds a predefined voltage. Accordingly, the shunt regulator rectifier operates in two modes. In mode one, when the output is below a predefined voltage, the AC input is rectified and passed on to the output. In mode two, when the output is above a predefined voltage, AC input is shunted.
A gate driver 130, 132, 134 is provided and configured to receive inputs from a phase detector 140, 142, 144 and a shunt controller 160, 162, 164 to control operation of the MOSFET. A voltage detector 150 is provided and configured to detect output voltage of the shunt regulator rectifier. The voltage detector provides a suitable signal to the shunt controller to commence second mode in case the output voltage is more than the predefined threshold voltage. The phase detector is configured to receive the AC input and detect whether the incoming phase is in positive half or in negative half of its cycle. Based on the phase of the AC input, a suitable signal is provided to the gate driver. Outputs from the shunt controller and phase detector are OR'ed 170, 172, 174 and provided to the gate driver. Accordingly, either the shunt controller or the phase detector may control the operation of the MOSFET.
It may be noted that during rectification of negative half of the AC input, the phase detector gives a suitable signal to the gate driver to turn the MOSFET ON to minimize voltage drop across its terminals, thereby reducing the heat generated in the MOSFET. Accordingly, appropriate detection of phase of the AC input in a shunt regulator rectifier is an important feature.
While the phase detector detects phase of AC input and provides a corresponding signal to the gate driver, it is observed that the phase detectors invariably have instability in their output around zero crossing of the phase input. When a phase detector detects that a phase is entering negative half of cycle, it commands the gate driver to turn ON MOSFET. Thus, when MOSFET is turned ON, it brings potential of the phase very close to ground voltage. Consequently, the phase detector tends to turn OFF its command because it does not see the phase voltage to be negative anymore. As soon as this command is withdrawn, the phase voltage goes negative again causing the phase detector to turn ON the MOSFET. This phenomenon continues over and over till the phase voltage enters deep into negative cycle. This instability causes the output of the phase detector to rapidly switch its output high and low during each transition of the phase from positive cycle to negative cycle and vice-versa. Consequently, such unstable input to gate driver will cause instability in the MOSFET thereby creating uncertainty in working of the shunt regulator rectifier. This can also cause failure of the MOSFET
In view of the above, there is a need in the art to address at-least the aforementioned shortcomings.